Following the battle of Plassey in 1757, the British East India Company pursued a monopoly on production of Indian opium. For the next 50 years opium trade would be the key to their subcontinent. Importing opium to the Chinese was actually illegal by the Chinese law. So the East India Company established an elaborate trading scheme partially relying on legal markets, and partially leveraging illicit ones. They would bring in opium hidden on British ships then smuggled into China. British exports of opium into China grew from 15 tons in 1730, to 75 tons in 1773. In 1799 the Chinese empire reinstated the ban on opium.